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Abstract:

A golf club head enables the initial velocity of a ball to be increased
and enables the carry to be lengthened. In some example structures, the
golf club includes a face plate formed from metal and club head body
(e.g., a crown and sole) formed from fiber reinforced plastic. A weighted
body is provided inside the rearmost portion of the golf club head and a
low rigidity portion whose width becomes gradually narrower as it
approaches the rearmost portion is provided in the crown extending from
the vicinity of the face plate to the rearmost portion.

Claims:

1. A golf club head, comprising: a face plate formed from metal; a crown
formed from fiber reinforced plastic attached to the face plate, wherein
the crown includes a low rigidity portion extending from a vicinity of
the face plate toward a rearmost portion of the golf club head, wherein
the low rigidity portion has a width that becomes gradually narrower as
it extends toward the rearmost portion; a sole formed from fiber
reinforced plastic attached to the face plate and the crown; and a
weighted member provided inside a space defined by the crown, sole, and
face plate, wherein the weighted member is provided at the rearmost
portion of the golf club head.

2. A golf club head according to claim 1, wherein the low rigidity
portion is provided on a convex portion of the crown so as to protrude
from a main surface of the crown.

3. A golf club head according to claim 1, wherein a Young's modulus of
the fiber reinforced plastic forming the crown is 10 to 100 GPa.

4. A golf club head according to claim 1, wherein a thickness of the
crown is in a range from 0.4 to 2 mm.

5. A golf club head according to claim 1, wherein a mass of the weighted
member is in a range from 10 to 50 grams.

6. A golf club head according to claim 1, wherein the low rigidity
portion is formed between a first high rigidity portion located adjacent
a first side of the low rigidity portion and a second high rigidity
portion located adjacent a second side of the low rigidity portion,
wherein the low rigidity portion has a lower rigidity than the first high
rigidity portion and the second high rigidity portion.

7. A golf club head according to claim 6, wherein the first high rigidity
portion includes a first rib having a greater thickness than a thickness
of the low rigidity portion, and the second high rigidity portion
includes a second rib having a greater thickness than the thickness of
the low rigidity portion.

8. A golf club head according to claim 7, wherein the first rib extends
from a main surface of the crown in a direction away from the space, and
the second rib extends from the main surface of the crown in a direction
away from the space.

9. A golf club head according to claim 7, wherein the first rib extends
from a main surface of the crown in a direction toward the space, and the
second rib extends from the main surface of the crown in a direction
toward the space.

10. A golf club head according to claim 6, wherein the low rigidity
portion is formed from a thinner material than a material making up a
major portion of the crown surface.

11. A golf club head according to claim 6, wherein the low rigidity
portion is formed from a lower rigidity material than a material making
up a major portion of the crown.

12. A golf club head according to claim 6, wherein the first high
rigidity portion and the second high rigidity portion are made from one
or more materials having a higher rigidity than a material making up a
major portion of the crown.

13. A golf club head according to claim 1, wherein the crown includes a
first layer of fiber reinforced plastic having the fibers aligned in a
first direction and a second layer of fiber reinforced plastic having the
fibers aligned in a second direction that is different from the first
direction.

14. A golf club head according to claim 13, wherein the first direction
is substantially orthogonal to the second direction.

15. A golf club head according to claim 14, wherein the first direction
is at an angle of approximately 0.degree. with respect to a hitting
surface of the face plate and the second direction is at an angle of
approximately 90.degree. with respect to the hitting surface.

16. A golf club head according to claim 14, wherein the first direction
is at an angle of approximately +45.degree. with respect to a hitting
surface of the face plate and the second direction is at an angle of
approximately -45.degree. with respect to the hitting surface.

17. A golf club, comprising: a golf club head according to claim 1; and a
shaft attached to the golf club head.

18. A golf club according to claim 17, further comprising: a grip
attached to the shaft.

19. A golf club head, comprising: a face plate; a club head body attached
to the face plate, wherein the club head body includes a deformation wave
transmitting system for transmitting at least a portion of the energy
contained in a deformation wave generated when a ball is struck by the
golf club head away from and toward the face plate; and a reflecting
member for reflecting at least a portion of the energy of the deformation
wave incident thereon back to the face plate via the deformation wave
transmitting system.

20. A golf club head according to claim 19, wherein the deformation wave
transmitting system extends from a vicinity of the face plate toward a
rearmost portion of the golf club head, wherein the deformation wave
transmitting system has a width that becomes gradually narrower as it
extends toward the rearmost portion and wherein the deformation wave
transmitting system is provided on a convex portion of the club head body
so as to protrude from a main surface of the club head body.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of U.S. patent
application Ser. No. 12/829,541 entitled "Golf Clubs and Golf Club
Heads," which was filed on Jul. 2, 2010 which is a divisional application
of U.S. patent application Ser. No. 11/773,323 entitled "Golf Clubs and
Golf Club Heads," which was filed on Jul. 3, 2007 (now U.S. Pat. No.
7,775,903) which is a continuation application of U.S. patent application
Ser. No. 10/935,744 entitled "Golf Clubs and Golf Club Heads," which was
filed on Sep. 8, 2004 (now U.S. Pat. No. 7,258,625), and all of which are
herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to golf club heads and golf clubs
including such golf club heads, as well as to methods for making such
golf club heads. In at least some examples, golf club heads in accordance
with this invention will be formed from one or more metal members and one
or more fiber reinforced plastic (FRP) members.

BACKGROUND

[0003] Long carry and excellent directional stability are required in golf
clubs and their associated golf club heads. In order to satisfy these
requirements, a high degree of design freedom regarding the center of
gravity and moment of inertia is sought in the structure of the golf club
head. In recent years, in order to raise the degree of design freedom of
the center of gravity and moment of inertia, a composite type of golf
club head has been proposed in which a metal member is placed in a low
position and a fiber reinforced plastic member is placed in a high
position (see, for example, Japanese Patent No. 2773009 and Japanese Laid
Open Patent Publication Nos. 59-90578 and 2002-336389). These documents
are entirely incorporated herein by reference.

[0004] The carry when a golf ball is hit by a golf club head depends to a
large extent on the initial velocity of the ball. On the other hand, the
initial velocity of the ball depends on the amount of kinetic energy
transmitted to the ball from the golf club head. Accordingly, the carry
distance typically can be lengthened by increasing the amount of kinetic
energy that is transmitted to the ball.

[0005] Following on from this, in order to increase the amount of kinetic
energy that is transmitted to a golf ball, golf club heads have been
proposed that include special features in the structure of the club
head's face plate. See, for example, U.S. Pat. Nos. 6,354,962; 6,368,234;
and 6,398,666. These patents are entirely incorporated herein by
reference.

[0006] However, in these known golf club heads, because a large amount of
kinetic energy is expended in deforming the golf club head at the moment
the ball is hit, it has not been possible to sufficiently increase the
initial velocity of the ball so as to lengthen the carry.

SUMMARY

[0007] The present invention was conceived in view of the above
circumstances, and at least one aspect of this invention relates to
providing golf club head structures that enable an initial velocity of a
ball to be increased so as to thereby increase a driving distance of the
ball.

[0008] Golf club head structures according to at least some examples of
the present invention include a face plate formed from metal and at least
a portion of a club head body (e.g., a crown and sole) formed from fiber
reinforced plastic. A weighted body is provided inside a rearmost portion
of the golf club head, and a low rigidity portion is provided in the
crown of the club head extending from a vicinity of the face plate or a
side of the club head body toward the rearmost portion of the golf club
head, wherein a width of the low rigidity portion becomes gradually
narrower as it approaches the rearmost portion. The low rigidity portion
may act as at least one portion of a "deformation wave transmitting
system," and the weighted body may act as at least a portion of a
reflecting member for energy from the deformation wave.

[0009] In this type of golf club head structure, because the initial
velocity of a ball can be increased, the carry when a ball is hit by the
club head can be lengthened. Aspects of this invention also relate to
golf clubs including such club heads and to methods of making such club
heads.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete understanding of the present invention and certain
advantages thereof may be acquired by referring to the following
description in consideration with the accompanying drawings, in which
like reference numbers indicate like features, and wherein:

[0011] FIG. 1 is a cross-sectional view showing an example golf club head
structure according to the present invention;

[0012]FIG. 2 is a top view of the golf club head structure shown in FIG.
1, further illustrating a convex portion of the golf club head structure;

[0013]FIG. 3 is a cross-sectional view taken along line A-A' in FIG. 2;

[0014]FIG. 4 is a cross-sectional view showing one step in an example
procedure for manufacturing the golf club head structure shown in FIG. 1;

[0015]FIG. 5 is a cross-sectional view showing another step in an example
procedure for manufacturing the golf club head structure shown in FIG. 1;

[0016]FIG. 6 is a cross-sectional view showing another step in an example
procedure for manufacturing the golf club head structure shown in FIG. 1;

[0017] FIG. 7 is a cross-sectional view showing another example of a golf
club head structure according to the present invention;

[0018]FIG. 8 is a top view showing still another example of a golf club
head structure according to the present invention;

[0019]FIG. 9 is a cross-sectional view taken along the line B-B' in FIG.
8;

[0020]FIG. 10 is a cross-sectional view showing another example of a golf
club head structure according to the present invention;

[0021] FIG. 11 is a cross-sectional view showing yet another example of a
golf club head structure according to the present invention; and

[0022]FIG. 12 is a cross-sectional view showing another example of a golf
club head structure according to the present invention.

DETAILED DESCRIPTION

[0023] In the following description of various example embodiments of the
invention, reference is made to the accompanying drawings, which form a
part hereof, and in which are shown by way of illustration various
example devices, systems, and methods in which aspects of the invention
may be practiced. It is to be understood that other specific arrangements
of parts, example devices, systems, and methods may be utilized and
structural and functional modifications may be made without departing
from the scope of the present invention. Also, while the terms "top,"
"bottom," "front," "back," "side," "rear," and the like may be used in
this specification to describe various example features and elements of
the invention, these terms are used herein as a matter of convenience,
e.g., based on the example orientations shown in the figures. Nothing in
this specification should be construed as requiring a specific three
dimensional orientation of structures in order to fall within the scope
of this invention.

[0024] Various examples of golf club head structures according to the
present invention now will now be described.

[0025] FIG. 1 is a cross-sectional view showing a golf club head 1
according to a first example of the present invention. This example golf
club head structure 1 has a metal face plate 10 that has a face 11 and a
flange 13 that is formed extending from an edge of the face 11 toward a
side opposite from a hitting face 12 of the club head (i.e., the flange
13 extends in a direction away from the hitting face 12). The golf club
head 1 further includes a metal sole plate 20, a crown 30, and a sole 40.
The crown 30 and sole 40 of this example structure make up a main portion
of the club head body and are made from fiber reinforced plastic. A
weighted body 50 is provided inside a rearmost portion of the golf club
head structure 1. Here, the rearmost portion is the portion located
furthest to the rear of the golf club head 1 when the hitting face 12 of
the face plate 10 faces to the front.

[0026] The various parts of the golf club head may be secured together in
any desired manner without departing from the invention, including in
conventional manners known in the art. In this illustrated golf club head
1 example, the flange 13 of the face plate 10 and the crown 30 and the
sole 40 are adhered together at respective adhesion overlaps of each via
a film type adhesive agent 60. The crown 30 and sole 40 also may be
adhered together at respective adhesion overlaps of each in the vicinity
of the rearmost portion. Conventional adhesives may be used as are known
in the art.

[0027] The face plate 10 and sole plate 20 of this example golf club head
1 may be manufactured in any desired manner without departing from the
invention, including in conventional manners known in the art, such as by
casting, forging, machine cutting metal, etc. Also, while any desired
type of material may be used for the face plate 10 and/or sole plate 20
of the golf club head structure 1, examples of suitable materials that
may be used include titanium alloys, aluminum high strength alloys,
stainless steels, etc. In at least some examples, in view of its balance
between strength and specific gravity, titanium alloys advantageously may
be used. Also, the face plate 10 and sole plate 20 may be made from the
same material or from different materials without departing from the
invention. Additionally, the face plate 10 and the sole plate 20 may be
combined or separated. In particular, in at least some examples, because
it is possible to easily lower the center of gravity of the golf club
head 1, it may be preferable to use a material for the sole plate 20 that
has a higher specific gravity than that of the face plate 10. As a more
specific example, in at least some example club head structures 1,
stainless steel may be used for the sole plate 20 and titanium alloy may
be used for the face plate 10.

[0028] In order to increase the strength of the adhesion of the various
parts together, in at least some examples of the invention, the surfaces
of the face plate 10 and the sole plate 20 that are adhered to the crown
30 and/or sole 40 will previously undergo a roughening treatment (e.g.,
by blast processing, sanding, or the like) so that the surface roughness
("Ra") thereof is between 1 μm and 20 μm. Also, the surfaces
of the face plate 10 and sole plate 20 that are adhered to the crown 30
and/or sole 40 may undergo degreasing processing, e.g., using methyl
ethyl ketone, acetone, or the like, to further improve the bonding and
increase the strength of adhesion of these parts.

[0029] As noted above and illustrated in FIG. 1, the flange 13 of the face
plate 10 is the portion of the overall club head structure 1 by which the
face plate 10 is adhered to the crown 30 and/or to the sole 40. While any
desired flange 13 size may be used without departing from the invention,
some aspects of the flange 13 size can help improve the structure and/or
characteristics of the club head 1. For example, when the flange 13 is
long, the strength of adhesion between the flange 13 of the face plate 10
and the crown 30 and/or sole 40 increases, but if it is too long, the
weight of the golf club head 1 may increase too much. Accordingly, in at
least some example structures 1, the flange portion 13 will be designed
to have a length between 5 mm and 25 mm, and in some examples, the length
may be between 10 mm to 15 mm.

[0030] A hole 21 may be formed in the sole plate 20 for inserting a
pressure bag for use during the manufacture of the golf club head 1. The
hole 21 may be a threaded hole (also known as a "bladder hole"). When the
hole 21 is a threaded hole, after the pressure bag has been withdrawn
from the threaded hole 21, a screw that fits the threaded hole 21 can be
screwed into it enabling the hole 21 to be easily blocked and thereby
closed off. A screw having a large specific gravity, such as one made
from a tungsten alloy, may be used, as this enables the center of gravity
of the overall golf club head structure 1 to be lowered even further.

[0031] The crown 30 may be formed as a single body by laminating a
plurality of fiber reinforced plastic layers in which the reinforced
fibers of each layer are aligned unidirectionally. These fiber reinforced
plastic layers may be laminated such that the direction of the fiber
alignment in each layer is orthogonal (or substantially orthogonal) to
that of the layers sandwiching it. For example, layers in which the
reinforced fibers are arranged at an angle of 0° to the hitting
face 12 may be laminated alternatingly with layers in which the
reinforced fibers are arranged at an angle of 90° to the hitting
face 12. Alternatively, layers in which the reinforced fibers are
arranged at an angle of +45° to the hitting face 12 may be
laminated alternatingly with layers in which the reinforced fibers are
arranged at an angle of -45° to the hitting face 12. In at least
some examples, a structure in which layers whose reinforced fibers are
arranged at an angle of +45° to the hitting face 12 are laminated
alternately with layers whose reinforced fibers are arranged at an angle
of -45° to the hitting face 12 may enable an initial velocity of a
ball to be further increased when struck by the club head structure.

[0032] As shown in FIGS. 2 and 3, a convex portion 31 may be provided in
the crown 30. This convex portion 31 may be structured such that its
width becomes gradually narrower as it approaches the rearmost portion of
the club head structure 1, and it may protrude away from the club head
interior space, e.g., in a substantially vertically upward direction. The
convex portion 31, in at least some examples, may extend from the
vicinity of the face plate 10 and/or the sides of the crown 30 toward the
rearmost portion of the crown, at or near a location where the weighted
body 50 is provided.

[0033] As shown in FIG. 3, two high rigidity portions 32 (e.g., portions
whose thicknesses are greater than their surrounding portions and whose
rigidities are higher than their surrounding portions) are formed at edge
portions on both sides of the convex portion 31. In this manner, a low
rigidity portion 33 (e.g., a portion whose thickness and rigidity both
are less than those of the high rigidity portions 32) is formed between
the high rigidity portions 32. The configuration of the low rigidity
portion 33 corresponds to the configuration of the convex portion 31.
Accordingly, in this example structure, the low rigidity portion 33 has a
width that becomes gradually narrower as it approaches the rearmost
portion of the crown 30 and extends from the vicinity of the face plate
10 and/or the sides of the crown to the rearmost portion of the crown 30.

[0034] In use of the club head structure 1, a deformation wave may be
generated in the crown 30 when a ball is hit. However, by providing this
low rigidity portion 33, this deformation wave is transmitted along the
low rigidity portion 33. As a result, the deformation wave can be
transmitted efficiently to the weighted body 50. The low rigidity portion
33 of this example acts as a deformation wave transmission system that
transmits energy of the deformation wave away from and back toward the
face plate 10 (and toward and away from the weighted body 50 reflecting
member).

[0035] In at least some example club head structures 1 according to the
invention, the Young's modulus of the crown 30 will be in a range between
10 and 100 GPa. When the Young's modulus of the crown 30 is in this
range, the crown 30 typically may be deformed in a more suitable manner
so that the amount of kinetic energy transmitted to the ball can be
further increased.

[0036] The Young's modulus of the fiber reinforced plastic that forms the
crown 30 in this example structure may be measured using a fiber
reinforced plastic plate material obtained by the following method.

[0037] First, a fiber reinforced plastic plate material that is to be used
as a test piece is manufactured. In manufacturing this fiber reinforced
plastic plate material, a pre-preg of the same material as that used in
the manufacture of the fiber reinforced plastic that forms the crown 30
is used. This pre-preg is cut to a suitable size and laminated to form a
laminated body. The laminate structure and the alignment of the fibers of
the pre-preg of the laminated body are made the same as those of the
fiber reinforced plastic forming the crown. The laminated body for the
test plate is formed under the same temperature and under the same
pressure conditions as those employed when the golf club head is formed,
to thereby form a fiber reinforced plate for the Young's modulus testing.

[0038] Next, the method used for measuring the Young's modulus using this
fiber reinforced plastic plate material will be described. More
specifically, in this example, the Young's modulus of this fiber
reinforced plastic plate material is measured in a tension test as
described below.

[0039] In this measuring procedure, first, both ends of the fiber
reinforced plastic plate material (i.e., the test plate described above)
are gripped by a gripping tool, and tensile stress then is applied to the
fiber reinforced plastic plate material. At this time, the direction in
which the tensile stress is applied corresponds to a direction along a
line connecting a center point of the golf club head with the rearmost
portion of the club head if the fiber reinforced plastic plate material
had been incorporated into a crown 30 of a golf club head structure 1.

[0040] Next, the amount of strain experienced when this tensile stress is
applied is measured using a strain gauge, and a relationship between the
tensile stress and the amount of strain is plotted on a graph. Then, a
range in which the amount of strain is 0.1% to 0.3% of the amount of
absolute strain is extracted from this graph. Because the graph is
essentially a straight line in this range, the inclination (or slope) of
the graph is determined, and this inclination is taken as the Young's
modulus of the fiber reinforced plastic material.

[0041] In at least some example club head structures 1, the thickness of
the crown 30 will be maintained in a range between 0.4 and 2 mm. When the
thickness of the crown 30 is 0.4 mm or more, the crown 30 typically
deforms more suitably and remains structurally stable. As a result, not
only can the amount of kinetic energy transmitted to the ball be further
increased, but the strength of the overall golf club head structure 1 can
be secured to a satisfactory degree. However, if the thickness of the
crown 30 exceeds 2 mm, typically the weight of the crown 30 will increase
to an undesired degree, and the center of gravity of the golf club head 1
tends to become somewhat higher. Additionally, the quantity of fiber
reinforced plastic required for the structure increases, which thereby
increases the manufacturing costs.

[0042] The sole 40 l may be formed as a single body by laminating a
plurality of fiber reinforced plastic layers in which the directions of
the reinforced fibers of each layer are aligned unidirectionally. These
fiber reinforced plastic layers may be laminated such that the direction
of fiber alignment of each layer is orthogonal to that of the layers
sandwiching it. For example, layers in which the reinforced fibers are
arranged at an angle of 0° to the hitting face 12 may be laminated
alternately with layers in which the reinforced fibers are arranged at an
angle of 90° to the hitting face 12. Angles of ±45° for
alternating layers also may be used without departing from the invention.

[0043] Any desired materials may be used for the fiber reinforced plastic
materials forming the crown 30 and/or sole 40 without departing from the
invention, including conventional materials known and used in the art.
Examples of the matrix resin that may be contained in the fiber
reinforced plastic that forms the crown 30 and/or the sole 40 include:
epoxy resin, vinyl ester resin, unsaturated polyester resin, polyimide
resin, maleimide resin, and phenol resin. Examples of the reinforcing
fiber include: carbon fiber, glass fiber, aramid fiber, boron fiber,
silicone carbide fiber, high strength polyethylene, PBO fiber, and
stainless steel fiber. Because of its excellent specific strength and
modulus, carbon fibers may be used as the reinforcing fiber in at least
some examples of this invention.

[0044] Likewise, any material may be used for the weighted body 50 without
departing from the invention. In at least some examples of the invention,
the weighted body 50 may be comprised of a metal having a large specific
gravity, such as tungsten, copper, lead, or the like. In some examples, a
resin combined with particles of tungsten or copper may be used (e.g.,
such materials can have favorable formativeness properties). As the resin
in such materials, a matrix resin the same as that used for the fiber
reinforced plastic of the crown 30 or sole 40 may be used, as in this
manner the weighted body 50 may be easily integrated into the structure
with the crown 30 and/or the sole 40. The weighted body 50 may be
structured and positioned so that it enables a deformation wave generated
in the crown 30 and transmitted by the transmission system to be
reflected back forward toward the front of the club head structure 1 and
toward the face plate 10. In this manner, at least some of the energy
included in the deformation wave as a result of hitting the ball can be
returned as kinetic energy to the ball via the reflected wave.

[0045] Weighted bodies 50 of various different weights also may be used
without departing from this invention. For example, in some example
structures 1, the mass of the weighted body 50 will be in the range of 10
to 50 g. In at least some golf club head structures 1, if the mass of the
weighted body 50 is 10 g or more, the deformation wave can be reflected
more efficiently. As a result, the amount of kinetic energy that acts on
the ball can be further increased, as described above. However, if the
mass of the weighted body 50 exceeds 50 g, the golf club head 1 may
become excessively heavy and more difficult to use, at least in some
example structures.

[0046] The adhesive agent 60 may be of various different compositions
without departing from the invention. In at least some examples, the
adhesive agent 60 may be a film type adhesive agent having a uniform
thickness. When such an adhesive agent is used, it is more difficult for
irregularities to be generated and consistent adhesion strength can be
obtained more easily. Examples of suitable resins for forming the film
type adhesive agent 60 include, but are not limited to: epoxy resin,
polyester resin, and acrylic resin. Epoxy resins are used in at least
some examples of this invention because of their excellent adhesion
strength. More specifically, in at least some examples of the invention,
the epoxy resin composition may contain an elastomer component and a
hardening agent component in addition to the epoxy resin component.
Specific examples of suitable elastomer components for use in accordance
with at least some examples of this invention include carboxy-terminated
butadiene acrylonitrile copolymers (CTBN) and the like.

[0047] Film type adhesive agent 60, when used, also may be modified to
contain a base material formed from fabric, such as an unwoven fabric or
a woven fabric. When the film type adhesive agent 60 contains a base
material such as a fabric, the ease of handling and adhesiveness thereof
may be improved. Moreover, even if stress is generated in the adhesive
agent after it has hardened so that minute cracks are generated, the
fabric material may help prevent the cracks from extending or developing
further. As a result, the breaking strength of the adhesive agent can be
improved. Examples of materials useful as the unwoven and woven fabrics
for the base material of the film type adhesive agent 60 include:
polyester fiber, nylon fiber, aramid fiber, acrylic fiber, and glass
fiber.

[0048] An example method of manufacturing a golf club head according to
the above example now will be described in more detail. First, a metal
face plate having a face and a flange, and a metal sole plate are
separately obtained, e.g., by casting, forging, machine cutting metal, or
the like.

[0049] Next, in preform manufacturing steps, a first preform is
manufactured by preliminarily forming a pre-preg into the configuration
of the sole. In addition, a second preform is manufactured by
preliminarily forming a pre-preg into the configuration of the crown.
When manufacturing the first preform (the sole preform in this example),
an aperture portion is formed such that a threaded hole that is formed in
the sole plate is not blocked. In this context, the term "preliminarily
forming" or "preliminary forming" refers to the laminating of a plurality
of pre-pregs so as to form a single body using the adhesive force
thereof, and then forming this into a configuration whose outline is
close to that of the ultimate crown or sole.

[0050] In manufacturing these preforms, before the "preliminary forming"
steps, it is preferable that breakage lines be formed in advance in the
pre-pregs. By forming the breakage lines in advance in the pre-pregs,
when the stacked pre-pregs are undergoing the preliminary forming steps,
the configurations of the crown and sole, which are curved
configurations, are easily formed by adhering together end portions of
the breakage lines.

[0051] Next, in an assembly step, as shown in FIG. 4, a bottom surface of
the first preform 71 is adhered to a top surface of the sole plate 20 via
a film type adhesive agent 60. In addition, the first preform 71 and the
flange 13 of the face plate 10 are adhered together via a film type
adhesive agent 60. At this time, the reinforcing fibers in the first
preform 71 are aligned, in their respective layers, to 0° and
90° relative to the hitting face 12. Next, a pre-preg 72 that has
been laminated such that the direction of alignment of the reinforcing
fibers thereof is orthogonal to that of the hitting surface 12 is further
adhered in the vicinity of the contact portion between the first preform
71 and the flange 13.

[0052] A metal-containing compound next is prepared by mixing a powder of
a metal having a high specific gravity (such as tungsten or copper) in a
precursor of a matrix resin. This metal-containing compound then is
formed into a belt shape and is adhered to the inside of the rearmost
portion of the first preform 71 so as to form a weighted body preform 73.

[0053] Next, as shown in FIG. 5, a pressure bag 22 is inserted via hole 21
in the sole plate 20. While any desired material may be used at the
pressure bag 22, examples of suitable materials include: silicone rubber,
nylon, and polyester.

[0054] The second preform 74 (for the crown) then is placed on top of the
first preform 71, and the second preform 74 and the flange 13 of the face
plate 10 are adhered together via a film type adhesive agent 60. At this
time, the reinforcing fibers in the second preform 74 are aligned in
their respective layers at angles of +45° or -45° to the
hitting face 12. Next, a pre-preg 75 whose reinforcing fibers have been
aligned in their respective layers at angles of +45° or
-45° to the hitting face 12 is adhered to the vicinity of the
contact portion between the second preform 74 and the flange 13. As a
result of the above steps, a molded product precursor 80 is obtained.

[0055] Next, in a bladder molding step, bladder molding is performed on
this molded product precursor 80. As a more specific example, as shown in
FIG. 6, the molded product precursor 80 is placed inside a mold 90 formed
by an upper mold 90a and a lower mold 90b. The mold 90 then is closed,
and the pressure bag 22 is inflated by supplying air (or other gas) to
the pressure bag 22. A groove whose width becomes gradually narrower as
it approaches the rearmost portion of the club head is formed at a
position in the upper mold 90a of the mold 90 that corresponds to a
portion extending from the vicinity of the face plate 10 or a side of the
second precursor 74 of the molded product precursor 80 to the rearmost
portion thereof.

[0056] As a result, the first preform 71 and the second preform 74 are
pressed against the mold 90 by the inflated pressure bag 22. At the same
time, the matrix resins of the respective preforms 71 and 74 undergo heat
curing and are consequently molded and set. At the time of this molding,
the precursor of the weighted body preform 73 that is adhered to the
inside of the rearmost portion of the first preform 71 is cured so as to
form the weighted body 50. Moreover, because a portion of the top surface
of the second preform 74 is pressed into the groove in the upper mold
90a, a convex portion whose width becomes gradually narrower as it
approaches the rearmost portion of the club head is provided in the crown
extending from the vicinity of the face plate or the side of the crown
toward the rearmost portion.

[0057] The mold 90 then is opened and the resulting molded product is
extracted. In addition, the pressure bag 22 is taken out via the hole 21.
Finally, a screw is screwed into the hole 21 in the sole plate 20 so as
to close off the threaded hole and thereby enable a golf club head
structure to be obtained.

[0058] In the above-described example, a weighted body 50 is provided
inside the rearmost portion of the golf club head 1, and a low rigidity
portion 33 whose width gradually becomes narrower as it approaches the
rearmost portion of the crown 30 is provided in the crown 30 (see, for
example, FIGS. 1-3). When a ball is hit with this golf club head 1, the
resulting shock creates a deformation wave in the crown 30 that moves
toward the rear of the club head structure 1. However, in this golf club
head structure 1, the deformation wave is transmitted to the rearmost
portion along the low rigidity portion 33, and at least some portion of
the energy in the deformation wave then is able to be reflected back
toward the front of the club head 1 by the weighted body 50 provided in
the rearmost portion of the crown 30 (via the deformation wave
transmission system 33). It also is possible to make this reflection wave
act on the ball via the face plate 10. Accordingly, because it is
possible to transmit this reflected energy to the ball (i.e., energy that
has hitherto been lost due to deformation), it is possible to suppress,
at least to some degree, the loss of kinetic energy that is caused by
deformation of the golf club head 1. Namely, because the amount of
kinetic energy that is transmitted to the ball is increased (due to the
reflected wave), it is possible to increase the ball's initial velocity
and thereby lengthen the carry.

[0059] One example of a desirable embodiment of the present invention is
described above. However, as those skilled in the art will readily
appreciate, the present invention is not limited to this example
embodiment. Additions, omissions, substitutions, and other modifications
may be made without departing from the spirit or scope of the present
invention. Various additional example golf club head structures according
to the invention are described in more detail below.

[0060] Another example golf club head structure according to the invention
is illustrated in FIG. 7. In this example structure, a concave portion
101, which is recessed into the interior space of the club head, e.g., in
a substantially vertical direction from the top surface of the crown 30,
is provided. This concave portion 101 may extend from the vicinity of the
face plate or a side of the crown 30 toward and to the rearmost portion
of the crown 30 in a manner similar to the convex portion 31 of the above
example structure. The width of this concave portion 101 may be
structured so as to become gradually narrower as it approaches the
rearmost portion of the crown 30. By providing this type of concave
portion 101, two high rigidity portions 102, whose thicknesses are
greater than those of the surrounding portions and whose rigidities are
higher than those of the surrounding portions, are formed. In addition a,
low rigidity portion 103 (e.g., whose width becomes gradually narrower as
it approaches the rearmost portion of the crown 30 and whose thickness
and rigidity are both less than those of the high rigidity portions 102)
is formed between the high rigidity portions 102.

[0061] Another example golf club head structure according to the invention
is illustrated in conjunction with FIGS. 8 and 9. In this example
structure, two raised ribs 104 are provided in the crown 30 that extend
from the vicinity of the face plate 10 and/or a side of the crown 30 to
the rearmost portion of the crown 30. In the illustrated example, the
space between the ribs 104 becomes gradually narrower as the ribs 104
approach the rearmost portion of the crown 30. Because the portions of
the crown 30 where the ribs 104 are provided have an increased thickness,
these portions 104 become high rigidity portions whose rigidity is higher
than that of their surrounding portions. Moreover, because the portion of
the crown 30 that is included between the ribs 104 is thinner than the
portions where the ribs 104 are provided, this intermediate portion forms
a low rigidity portion 105 of the crown 30 that has a low rigidity as
compared to the ribs 104. Because the space between the two ribs 104
becomes gradually narrower as the ribs 104 approach the rearmost portion
of the crown 30, the width of the low rigidity portion 105 that is
included between these ribs 104 becomes gradually narrower as it
approaches the rearmost portion of the crown 30.

[0062] Many variations in the structure illustrated in FIGS. 8 and 9 may
be used without departing from the invention. For example, as illustrated
in FIG. 9, the ribs 104 of this example structure are provided so as to
face toward the outside of the golf club head (i.e., the ribs 104 are
raised on the outer surface of the crown 30 and extend outwardly).
However, if desired, some or all of the ribs 104 may be provided so as to
face toward the inside of the golf club head (i.e., one or more of the
ribs 104 may be raised out of the inner surface of the crown 30 and
extend toward the inside of the club head), and the same effect increased
rigidity will be achieved. Furthermore, while the structure illustrated
in FIG. 9 shows the ribs 104 as solid members, the ribs 104 also may be
hollow without departing from the invention. Additionally, the ribs 104
may be integrally formed as part of the crown 30 structure (as a unitary,
one-piece construction), or they may be separate elements attached to the
crown 30 in some manner.

[0063]FIG. 10 illustrates still another example golf club head structure
according to the invention. As shown in FIG. 10, it also is possible to
provide two high rigidity portions 106 without providing a raised region
as shown in some of the other example embodiments. More specifically, as
shown in FIG. 10, two high rigidity portions 106 are formed from a
material having a higher rigidity than that of their surrounding
portions. These high rigidity portions 106, while the same thickness as
the remainder of the crown 30, extend from the vicinity of the face plate
and/or the side of the crown to the rearmost portion of the crown 30.
Again, the space 107 between the high rigidity portions 106 becomes
gradually narrower as it approaches the rearmost portion of the crown 30.
Because the portion 107 between the high rigidity portions 106 has a
lower rigidity than that of the surrounding high rigidity portions 106,
this portion 107 forms a low rigidity portion 107 whose width becomes
gradually narrower as it approaches the rearmost portion of the crown.

[0064] Another example golf club head structure according to this
invention is illustrated in FIG. 11. Rather than providing a raised or
thicker portion of the crown 30 as the high rigidity portions, as
illustrated in some of the example structures above, it also is possible
to provide a portion of the crown 30 that is thinner than its surrounding
portions and that extends from the vicinity of the face plate of the
inner (or outer) surface of the crown 30 toward the rearmost portion of
the crown 30. The width of this thin portion 108 may become gradually
narrower as it approaches the rearmost portion of the crown 30. Because
the rigidity of the thin portion 108 is less than that of its surrounding
portions, it forms a low rigidity portion 108 and functions as a
deformation wave transmission system in the manner of the low rigidity
portions described above.

[0065] As shown in FIG. 12, it also is possible to provide a low rigidity
portion 109 by forming a portion 109 of the crown 30 from a material
having a lower rigidity than that of its surrounding portions and having
a lower rigidity than the remainder of the crown 30. This portion 109 may
extend from the vicinity of the face plate and/or the sides of the crown
30 toward the rearmost portion of the crown, as generally described
above. The width of this low rigidity portion 109 may become gradually
narrower as it approaches the rearmost portion of the crown 30. This type
of low rigidity portion 109 also may be provided by providing high
rigidity portions 110 that are formed from a material having a high
rigidity in portions on both sides of the low rigidity portion 109.

[0066] Deformation waves also can be efficiently transmitted to and/or
away from a weighted body 50 via the low rigidity portions as described
in conjunction with FIGS. 7-12 above.

[0067] Moreover, in the above described examples, the direction of
alignment of the reinforced fibers in the crown 30 may be controlled such
that layers with reinforced fibers arranged at an angle of 0° to
the hitting face are laminated alternately and sandwiched between layers
with reinforced fibers arranged at an angle of 90° to the hitting
face. Alternatively, the direction of alignment of the reinforced fibers
in the crown 30, in at least some examples of the invention, may be
controlled such that layers with reinforced fibers arranged at an angle
of +45° to the hitting face are laminated alternately and
sandwiched between layers with reinforced fibers arranged at an angle of
-45° to the hitting face. In at least some example structures
according to the invention, it is sufficient if the angles of orientation
of the layers lie within a range from 0° to ±90°. Within
this range, in at least some examples, it is preferable if the range be
maintained between ±10° to ±80°, as this may provide
a faster initial ball velocity. Likewise, the direction of the
orientation of the reinforced fibers in the sole also may be maintained
in the range of 0° to ±90° relative to the hitting face,
and in some examples between ±10° to ±80°, although
other arrangements and orientation directions also may be used without
departing from the invention.

[0068] If desired, in at least some examples of the invention, the
reinforcing fibers contained in the fiber reinforced plastic need not be
aligned within a given layer and/or need not be arranged in orthogonally
arranged unidirectional layers. Moreover, in at least some example
structures, woven fabrics also may be used.

[0069] In addition, in the example structures described above, the flange
13 of the face plate 10 and the crown 30 and sole 40, and also the sole
plate 20 and the sole 40, are adhered together using a film type adhesive
agent. Other means of securing these members together also may be used,
however, without departing from the invention. For example, one or more
mechanical connectors may be used. Welding or soldering also may be used,
if desired. As still another example, a liquid type adhesive agent may be
used without departing from the invention. In examples where a liquid
type adhesive agent is used, when forming a three-dimensional shape such
as a golf club head, sufficient care must be taken to provide the coating
in a relatively uniform thickness and width. Coating unevenness and/or
thickness unevenness of the adhesive agent may, in at least some
instances, cause the adhesive strength of the adhesive coating to be
reduced, thereby making it difficult to obtain a golf club head having a
consistent strength.

[0070] If desired, it also is possible to provide a decorative layer or
indicia on any surface of the golf club head, including the hitting face.
When a decorative layer or indicia is provided, the design of the golf
club head may be more aesthetically pleasing. Printing, engraving, and
other conventional marking systems and methods may be used to provide the
decorative information or indicia on the club head, if desired.

[0071] Various examples of the production of golf club head structures,
including structures according to the present invention and results
obtained using such structures, are provided below. Those skilled in the
art will recognize, however, that the scope of the present invention is
in no way limited to these examples or the results achieved thereby.

EXAMPLE 1

[0072] First, a titanium alloy face plate equipped with a face having a
thickness of 2.8 mm and a flange having a thickness of 1.5 mm and a
stainless steel (SUS 314) sole plate having a thickness of 1.5 mm were
separately forged. Next, surface roughening treatments were performed on
the flange surfaces of the sole plate and the face plate by blast
working, and these surfaces then were degreased using acetone.

[0073] Next, in a first preform manufacturing step, pre-pregs (made of
PYROFIL® TR350, manufactured by Mitsubishi Rayon Co., Ltd.) with
carbon fibers arranged in two intersecting directions were impregnated
with epoxy resin and were formed in advance into the general
configuration of the sole of the golf club head, thereby forming a first
preform (having a thickness of 1.5 mm). At this time, an aperture portion
was formed in the first preform so that the threaded hole in the sole
plate would not be obstructed by the sole preform.

[0074] Next, in an assembly step, as is shown in FIG. 4, the bottom
surface of the first preform 71 was adhered to the top surface of the
sole plate 20 via a film type adhesive agent 60. In addition, the first
preform 71 was adhered to the flange 13 of the face plate 10 via a film
type adhesive agent 60. Next, a pre-preg 72 whose carbon fibers were
aligned in a direction running 0° relative to the hitting face 12
and that had a thickness of 0.25 mm was further adhered in the vicinity
of the contact portion between the first preform 71 and the flange 13.

[0075] A tungsten powder then was mixed in an epoxy resin composition, and
the resulting tungsten-containing mixture was formed into a belt shape
having a width of 10 mm. Next, 30 g of this tungsten-containing mixture
that was formed into a belt shape was measured out and was adhered to the
inside of the rearmost portion of the first preform 71. As a result, a
weighted body preform 73 was obtained.

[0076] Subsequently, as is shown in FIG. 5, a pressure bag 22 formed from
silicone rubber was inserted into the first preform 71 via the threaded
hole 21 in the sole plate 20 (and the corresponding opening provided in
the first preform 71).

[0077] In the second preform manufacturing step, four layers of the above
described pre-pregs were laminated such that the directions of the carbon
fibers thereof were aligned and arranged in separate layers at angles of
±45° relative to the hitting face. As a result, a second
preform (having a thickness of 0.5 mm) that was preliminarily formed in
the shape of the crown of a golf club head was obtained. This second
preform 74 then was placed on top of the first preform 71, and the second
preform 74 and the flange 13 of the face plate 10 were adhered together
via a film type adhesive agent 60. Next, a pre-preg 75 having a thickness
of 0.5 mm and whose carbon fibers had been aligned at angles of
±45° relative to the hitting face 12 was further adhered at the
vicinity of the contact portion between the second preform 74 and the
flange 13. In this manner, a molded product precursor 80 was obtained.

[0078] Next, an internal pressure molding step, as shown in FIG. 6, was
performed. More specifically, the molded product precursor 80 was placed
inside a mold 90 formed by an upper mold 90a and a lower mold 90b. The
mold 90 then was closed by a hydraulic press, and the pressure bag 22
then was inflated by supplying air to the pressure bag 22. The upper mold
90a that was used in this example had a groove having a depth of 3 mm and
whose width became gradually narrower as it approached the rearmost
portion of the crown. This groove was provided at a position that
corresponded to a portion of the crown extending from the vicinity of the
face plate 10 of the molded product precursor 80 to the rearmost portion
thereof.

[0079] The first preform 71 and the second preform 74 were pressed against
the mold 90 by the inflated pressure bag 22. At the same time, the matrix
resins of the respective preforms underwent heat curing and were
consequently molded and set. As a result of this molding, the first
preform 71 and the pre-preg 72 formed the sole 40, and the second preform
74 and the pre-preg 75 formed the crown 30. In addition, the weighted
body preform 73 formed the weighted body 50, and a convex portion whose
width became gradually narrower as it approached the rearmost portion of
the club head structure was provided in the crown 30 extending from the
vicinity of the face plate to the rearmost portion of the crown 30.

[0080] Next, the mold was opened, and the obtained molded product was
extracted. In addition, the pressure bag 22 was taken out via the hole
21. Finally, a tungsten alloy screw was screwed into the hole 21 in the
sole plate so as to close off the threaded hole and thereby enable a golf
club head to be obtained.

EXAMPLE 2

[0081] A golf club head was obtained in the same manner as in Example 1
except that no groove was formed in the upper mold. This resulting golf
club head was the same as the golf club head of Example 1 except that no
convex portion was provided.

EXAMPLE 3

[0082] A golf club head was obtained in the same manner as in Example 2
except that a second preform was obtained by laminating pre-pregs such
that the directions of the carbon fibers thereof were alternately
0° and 90° relative to the hitting face.

EXAMPLE 4

[0083] In order to make a comparison with Examples 1 to 3, a titanium
alloy golf club head whose crown had a thickness of 0.5 mm and whose sole
had a thickness of 1.5 mm was used.

[0084] Measurement of Initial Velocity of Ball:

[0085] Using the golf club heads of Examples 1 to 4, the initial velocity
of a golf ball that was hit at a head velocity of 50 m/sec was measured
30 times using a laser light method. The average values that were
obtained are shown in Table 1.

[0086] As shown in Table 1, the ball initial velocity obtained using a
golf club head in which a weighted body was provided inside the rearmost
portion was faster than that obtained using a titanium alloy golf club.
From this result, it can be assumed that the carry would be lengthened.
In particular, the golf club head of Example 1, in which the directions
of alignment of the reinforcing fibers in the crown are ±45°
relative to the hitting face, and in which a convex portion is provided
so that a low rigidity portion is formed, providing the fastest ball
initial velocity. Therefore, it can be assumed that this golf club head
would enable the driving distance to be lengthened the most.

[0087] Golf club heads of the type described above may be formed into golf
clubs by attaching a shaft to the head and a grip to the shaft in any
desired manner, including in conventional manners known in the art. For
example, the shaft may be attached to the head using mechanical
connectors, threads, screws, bolts, adhesives, and/or the like. Grips
also may be attached to the shafts using adhesives, or the like.
Conventional shaft materials (e.g., steel, graphite, etc.) and grip
materials (e.g., polymers, synthetic rubbers, leathers, etc.) also may be
used without departing from this invention.

[0088] While the invention has been described with respect to specific
examples including presently preferred modes of carrying out the
invention, those skilled in the art will appreciate that there are
numerous variations and permutations of the above described systems and
methods. Thus, the spirit and scope of the invention should be construed
broadly as set forth in the appended claims.